frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 1

The Munich Stability ProjectGarching, 10th May 2010

FOCES, a testbed for high stabilityspectroscopy

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 2

At the very beginning ...• ... my first spectrograph!• 1987 as a school

project• Objective prism +

normal camera

19872009

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 3

Stability Project – Outline FOCES

– A few words on the instrument Why

– What degree of stability do we need What

– Spectrograph stability– Illumination stability– Fiber stability– FOCES as testbed

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 4

FOCES – an instrument introduction• Calar Alto 2.2m

(1997-2009)• R=46000/64000

on 24/15μm CCD• L-N2 cooled• Moving parts (slit,

grating, prisms..)• Un-stabilized• S/N=100 for 10th

mag G-star: 1h

• Wendelstein 2m (2010/2010...)

• R=70000on 13.5μm CCD

• Peltier cooled • No moving parts

• P,T stabilized• S/N=100 for 10th

mag G-star: 1h

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 5

Who?• MPQ + Lehrstuhl Hänsch (@LMU)

– Theodor Hänsch– Thomas Udem– Tilo Steinmetz

• Menlo Systems– Ronald Holzwarth

• MPE + USM– Ralf Bender– Frank Grupp

• ESO

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 6

Why?• Precission radial velocity work aims for sub

m/s regime (planets, astro-seismology) – That's the speed of a pedestrian walking...

• 1m/s ≈ 1/3000 of a pixel on a R=70000 Échelle machine with 13.5μm pixel size

• We need enormous stability– Of the spectrograph itself (T,P,bend, …)– Of the spectrograph slit illumination

• Fiber illumination stability (seeing, guiding, coherent-incoherent light coupling)

• Fiber “throughput” stability (modes)

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 7

Spectrograph stability (1)• Two concepts:

– HARPS is kept in vacuum and is very well thermalized

– PEPSI is kept under constant – near environmen pressure – and also well thermalized

• FOCES based ZEMAX simulations on “what P,T stability do we need?”

– Strongly simplified– Intention is to understand “where things

happen”

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 8

Spectrograph stability (2)• A glimpse on the

results (dx vs. dP)• Almost linear• “Problem” arises

at the cross dis-perser prisms

• ±0.4hPa shouldbe a good stability goal

• This is achievedby PEPSI

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 9

Illumination stability (1)• A simple – non modal - view on the problem

• Illuminating a fiber under a certain angle → a ring with a slightly widened, but correlated angle

• Fibers have an angular memory• Changing the input -angular- distribution of

light changes the light distribution at the fiber exit→ Slit illumination changes!!!

• With modes the situation even becomes more granular and complex

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 10

Illumination stability (2)• As we will always experience seeing and

guiding variations we need:– Means of making an inhomogeneous beam

(more) homogenous

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 11

Throughput stability – modes (2)• What are fiber modes• Like microwaves are guided in a hollow waveguide …• … light is guided in a dielectric waveguide …• Suddenly we leave the field of ray optics!!!• Like in the hollow waveguide modes depend on geometry and size of the waveguide

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 12

Throughput stability – modes (3)

A real 100μm astronomicalfiber, illumi-nated with ared laserpointerM>10000

How do fiber modes look like?● Number of modes: M=22 R2

2 sin2arctan 12f

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 13

Throughput stability – modes (4) Modes are correlated with angles feeding the

spectrograph Each mode is

imaged to a certain position on the CCD

Moving modes result in moving spot centers

A certain spot=wavelength jitters !

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 14

Status – Stability project We took FOCES to our Munich labs this

January. Together with ESO (Luca) we have hired a

student (Anna) for the project We have re-assembled and aligned

FOCES in the last 3 days A pressure chamber is almost finished

(test-run planned in May) Heating installation has started and should

be completed by the end of next week

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 15

Outlook – Stability project As perfect normals frequency combs shall

be used as a reference to understand the bahaviour and physics of the system

We want to study: Pressure and temperature effects Fiber illumination effects Fiber coupling effects Fiber transport effects We will start with lab condition studies In 2012 we will move to Wendelstein

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 16

Stability – The end .... … or the beginning of a

better understanding We (astronomers)need

help! – The quantum optics

view on fibers– Better means on

“scrambling” light– New and better design ideas

Thank you for your time and dedication

frank@grupp-astro.de Frank GRUPP – Munich Stability Project Slide 17

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